Luminescent Semiconductor Quantum Dots (QDs) and Their Nanoassemblies as Bioprobes

Author

Chen, Yongfen

Document Type

Dissertation;

Keywords

Bioprobes; Nanoassemblies; Luminescent
Quantum dots

Abstract

Quantum dots (QDs) CdS and CdSe were synthesized in three different media including
reverse micelles, aqueous solution, and trioctylphosphine oxide/trioctylphosphine (TOPO/TOP).
Transmission electron microscope (TEM), X-ray diffraction (XRD), UV-VIS, fluorescence
spectroscopy and microscopy were used to characterize the QDs and their nanoassemblies. CdS
QDs synthesized in reverse micelles showed broad emission spectra. CdSe-CdS QDs with core
shell structure synthesized in aqueous solution showed more than 30% emission quantum yield.
CdSe-CdS QDs of different emission colors were prepared. CdSe and CdSe-ZnS QDs were also
synthesized in TOPO/TOP media. This synthesis route produced highly luminescent CdSe QDs
with over 50% emission quantum yield.
The application of QDs as ions probes and methods to encapsulate QDs in nanospheres including
micelles, glyconanospheres and silica nanospheres and the use of these nanospheres in bioassays
are described. CdS QDs capped with different ligands such as thioglycerol, cysteine and
polyphosphate showed different responses to biological relevant ions. The emission intensity of
polyphosphate capped CdS QDs was affected by all the tested ions and did not show a selective
response. On the other hand, the emission of thioglycerol capped CdS QDs was selectively
quenched by copper ions while the emission of cysteine capped CdS QDs was selectively
enhanced by zinc ions. Stern-Volmer equation was applied to correlate the emission intensity of
the CdS QDs and the copper ion concentration. A Lagmuir isotherm binding equation was used to describe the relation between the emission intensity of cysteine capped CdS QDs and zinc ion
concentration. The possible mechanism to explain the effects of capping ligands on CdS QDs
responses to ions is also discussed. CdSe QDs synthesized in TOPO/TOP media were
encapsulated in nanospheres for bioassay applications. The glyconanospheres contained a large
number of glucose residues on their surface and showed high binding activity towards the
lectinic protein Concanavalin A (Con A). Silica nanospheres containing hundreds of CdSe QDs
were functionalized with thiol groups to enable the conjugation of streptavidin to the
nanospheres. The streptavidin modified silica nanospheres were used as luminescent indicators
in a sandwich immunoassay for the detection of antiprotein A antibody. The advantages and
disadvantages of the nanospheres based bioassay are discussed.

The University of New Orleans and its agents retain the non-exclusive license to archive and make accessible this dissertation or thesis in whole or in part in all forms of media, now or hereafter known. The author retains all other ownership rights to the copyright of the thesis or dissertation.